Establishment and application of fluorescence labeled phage for rapid detection of Escherichia coli K1

Abstract:

[Background] Escherichia coli (E. coli) is one of the most common Gram-negative bacteria causing neonatal meningitis and poultry meningitis. The strain E. coli capsular K1 is an important pathogen. Current methods for detecting E. coli capsular K1 have some disadvantages.[Objective] A rapid detection method for E. coli capsular K1 was established by using the host specific phage PNJ1809-36. [Methods] Phage PNJ1809-36 was labeled with fluorescent dye SYBR gold, and 33 tested strains were infected by this fluorescent phage. The specificity was determined by observing the 33 test strains using the fluorescence microscopy. The sensitivity was determined by observing the host bacteria DE058 with gradient tenfold dilution after being infected with fluorescence labeled phage. Eight simulated feces were detected by fluorescent labeled phages. Moreover, the titer change and detection efficiency of fluorescent labeled phages stored at 4℃ in darkness were investigated. [Results] Among the 33 strains tested, 8 strains of 9 E. coli can be observed with fluorescence around the bacteria, but one could not be detected. No fluorescence was observed in 20 non-E. coli capsular K1 strains and 4 non-E. coli strains. The detection sensitivity was 100 CFU/mL. The detection results of 8 simulated fecal samples showed that fluorescence could be observed in 3 samples containing E. coli capsular K1, and no fluorescence could be detected in 5 samples without E. coli capsular K1. After stored at 4℃ for 4 months, the titer of fluorescence labeled phages showed no obvious decrease, and the detection efficiency did not change significantly. [Conclusion] The fluorescence labeled phage PNJ1809-36 could be used to detect E. coli capsular K1 rapidly and intuitively within 15 min.

Key words:phage;fluorescence labeling;Escherichia coli;detection;K1 capsule